The present invention relates to a method and apparatus for simulating the placement of a ribbon-like material on a generally cylindrical carcass (as used herein, carcass shall refer generally to a base structure) to build up a desired profile of the ribbon on the carcass. In the presently preferred embodiment described below, the ribbon is formed of rubber, has a trapezoidal profile and is placed on a tire carcass in accordance with a predetermined winding specification to build up a desired rubber profile on the carcass. While the invention will be described with reference to this particular application, it should be recognized that the method and apparatus can more broadly be applied to simulate any profile build up where a ribbon of known (constant or changing) profile is laid on any rotating carcass.
The present invention is particularly useful in simulating the manner in which an Orbitread (Orbitread is a trademark of AMF incorporated) tire treading machine (illustrated schematically in FIG. 1) builds a tread profile on a tire by placing ribbons of trapezoidal rubber on a rotating tire carcass (this may be either a bare carcass or a carcass having an old rubber profile in the case of retreads). As shown therein, an extruder 10 produces a continuous rubber ribbon 12 which is passed through a pair of rolling dies 14, 16 which compress the ribbon 12 into a trapezoidal shape (see FIG. 6). The ribbon is then threaded over idler rollers 18, 20 and 22 and applied to a guide roller 26 which presses the ribbon 12 onto the outer surface of the tire carcass. As shown in FIG. 2, the left-hand edge of the roller 26 is beveled to form a guide that ensures that the ribbon 12 will be placed onto the carcass at a desired lateral position of the carcass. The edge 28 of the roller 26 defines the specific point in which the left-hand edge of the ribbon 12 will be placed on the tire carcass 24 and will be referred to hereinafter as the edge guide.
As shown schematically in FIGS. 3A and 3B, the Orbitread tire winding machine causes the tire carcass 24 to rotate about its own axis 30, thereby taking up the ribbon 12 which is being extruded. By translating the tire laterally with respect to the edge guide 28, the ribbon 12 can be placed on different sections of the carcass 24. When the tire being wound is a bias tire, the carcass 24 is moved laterally along its spin axis 30 to vary the relative lateral position between the carcass 24 and the edge guide 28. When the tire being wound is a radial tire, the tire winding machine pivots the carcass 24 about a wind axis 32 which defines the center of a circle, an arc of which approximates the shape of the outer surface 34 of the tire. The tire winding machine varies the position of the wind axis 32 so as to adjust the wind radius W to approximate the particular shape of the outer surface 34 of the tire.
The manner in which the pivotal movement of the carcass about axis 32 changes the position at which the ribbon 12 is applied to the carcass can best be understood with reference to FIGS. 3A and 3B. In FIG. 3A, the carcass 24 is maintained at a 0.degree. reference position wherein the ribbon 12 is applied to the center of the carcass. In FIG. 3B, the carcass 24 has been rotated counterclockwise to cause the ribbon 12 to be placed on the left end of the carcass 24. In each case, the position of the edge guide 28 with respect to the outer surface of the carcass 24 determines where the rubber 12 will be laid. In the present commercial embodiment, the edge guide 28 remains stationary while the carcass 24 is translated. Obviously, the same result can be achieved by translating the edge guide 28 and maintaining the carcass 24 at a single location. In either case, it is the relative movement between the edge guide 28 and the carcass 24 which determines where the rubber 12 will be laid. In the following description, reference will be made to the azimuthal movement of the edge guide along the arc prescribed by the wind radius W. Such references are used to indicate relative movement between the edge guide 28 and the carcass 24, whether it is the edge guide or the carcass (or both) that is being translated.
Utilizing the Orbitread tire winding machine, a plurality of winds of the rubber ribbon (a wind being a single strip of the rubber ribbon 12 placed around a single revolution of the tire) is placed on the outer surface 34 of the tire to form a desired tire profile. Once the rubber has been built up to the desired profile, the tire is removed from the Orbitread tire winding machine and placed in a mold which both cures the rubber and forms the desired tread pattern.
A typical rubber profile of a tire build formed in accordance with the Orbitread tire winding process is illustrated in FIG. 4A. As shown therein, a plurality of ribbons 12 is placed on the carcass 24 to form the desired profile. The manner in which the profile is formed is determined by a winding specification which is entered by a programmer into the Orbitread machine and defines the relative lateral movement between the edge guide 28 and the carcass 24 during each revolution of the carcass about its spin axis 30. The winding specification for the cross-section illustrated in FIG. 4A is shown in FIG. 4B. The winding specification includes a plurality of segments, each of which describes the desired movement of the edge guide relative to the carcass 24 during that segment. In the first segment, the edge guide is maintained stationary (S=0.0) and the carcass 24 is rotated through one revolution (REV=1) to cause a single wrap to be placed on the carcass 24. Since the carcass 24 is initially in the position illustrated in FIG. 3B, a single ribbon 12 will be placed along the leftmost edge of the carcass 24. During the second segment, the edge guide is translated 2.25 inches as measured along the arc prescribed by the wind radius W during a total of 0.90 revolutions of the tire. In the presently available commercial embodiment of the Orbitread tire winding machine, movement of the edge guide 28 is linear (equally distributed) during each segment. The method and apparatus for simulating the winding process, therefore, assumes such linear movement. It should be recognized, however, that non-linear movement could also be utilized in the actual ribbon laying system and would be duplicated in the simulation process.
The process is continued for the entire winding specifications until all the wraps of ribbon 12 are applied to the carcass. The winding specification which is applied to the tire winding machine is developed by a trained programmer who has significant experience with the system and can make a fairly accurate guess as to what specification will produce a desired tire profile. Once the programmer has guessed at the required winding specification, he enters it into the tire winding machine and produces a test run. The tire formed in accordance with the proposed winding specification is then removed from the system and cut along its axis to examine the actual tire profile resulting from the entered specification.
While the programmer is normally fairly accurate, the actual profile of the tire produced by the specification developed by the programmer will normally vary from the desired profile 36 as shown in FIG. 4A. In this example, an excess amount of rubber is formed on the left-hand side of the profile as well as on the topside of the profile while a shortage exists on the upper right-hand corner of the profile. After examining the actual profile of the rubber laid by the Orbitread machine, the programmer will then revise the winding specification in a manner which he believes will correct the errors in the profile.
The new winding specification is then entered into the Orbitread machine which builds a new profile on a new carcass 24. The resulting rubber build is then examined by cutting the tire along its axis and comparing the actual profile with the desired profile. If necessary, the winding specification is again revised and the process repeated until the actual profile conforms to the desired profile 36 to a sufficient degree.
Using the foregoing procedure, the programmer is able to develop a desired winding specification which may then be used to build a tread layer on a large number of tires. This process, however, is time-consuming and wastes rubber due to the need to actually build a rubber profile on a tire carcass each time the winding specification is modified to see if the change in the winding specification produces the desired results in the rubber profile. This process also causes undesirable down time on the system since the machine cannot be producing usable tires while it is being used to test a new winding specification.